Delay circuits or timer circuits changing the state of output at a predetermined period of time after the elimination of input signals are employed in various control circuits and a typical circuit of this kind in the prior art is an integration circuit using a resistor 12 and a capacitor 14 as shown in FIG. 1. When continuous pulse waves 22 are inputted from an input terminal 10 in this circuit, each of the pulse waves is smoothed as shown by a waveform 24 through an integration circuit composed of the resistor 12 and the capacitor 14 and shaped in a buffer amplifier 18, and the waveform 26 outputted from an output terminal 20 forms a continuous waveform, that is, a rectangular wave 26. Since the output waveform takes a "1" level during input of the pulse waves 22 and turns to a "0" level at a time .DELTA.t after the input of the pulse waves have been interrupted, a gate can be opened or closed after the elapse of the time .DELTA.t from the interruption of the input by controlling the gate with the output.
If such a delay circuit is intended to be fabricated as an integrated circuit, however, it is difficult to set a time constant, accordingly, the delay time t to the order of milliseconds or more since the capacitance value of a capacitor that can be realized in an integrated circuit is limited only to several picofarads.